Data from: Predictive modelling of habitat selection by marine predators with respect to the abundance and depth distribution of pelagic prey

1. Understanding the ecological processes that underpin species distribution patterns is a fundamental goal in spatial ecology. However, developing predictive models of habitat use is challenging for species that forage in marine environments, as both predators and prey are often highly mobile and difficult to monitor. Consequently, few studies have developed resource selection functions for marine predators based directly on the abundance and distribution of their prey. 2. We analysed contemporaneous data on the diving locations of two seabird species, the shallow-diving Peruvian Booby (Sula variegata) and deeper diving Guanay Cormorant (Phalacrocorax bougainvilliorum), and the abundance and depth distribution of their main prey, Peruvian anchoveta (Engraulis ringens). Based on this unique data set, we developed resource selection functions to test the hypothesis that the probability of seabird diving behaviour at a given location is a function of the relative abundance of prey in the upper water column. 3. For both species, we show that the probability of diving behaviour is mostly explained by the distribution of prey at shallow depths. While the probability of diving behaviour increases sharply with prey abundance at relatively low levels of abundance, support for including abundance in addition to the depth distribution of prey is weak, suggesting that prey abundance was not a major factor determining the location of diving behaviour during the study period. 4. The study thus highlights the importance of the depth distribution of prey for two species of seabird with different diving capabilities. The results complement previous research that points towards the importance of oceanographic processes that enhance the accessibility of prey to seabirds. The implications are that locations where prey is predictably found at accessible depths may be more important for surface foragers, such as seabirds, than locations where prey is predictably abundant. 5. Analysis of the relative importance of abundance and accessibility is essential for the design and evaluation of effective management responses to reduced prey availability for seabirds and other top predators in marine systems.

1. 阐明支撑物种分布格局的生态过程，是空间生态学（spatial ecology）的核心研究目标之一。然而，对于海洋觅食物种而言，构建栖息地利用预测模型颇具挑战——因为捕食者与猎物通常均具有极强的移动性，且难以开展监测。因此，鲜有研究直接基于猎物的丰度与分布，为海洋捕食者构建资源选择函数（Resource Selection Functions）。
2. 本研究整合了同步监测数据，涵盖两种海鸟的潜水位置信息：分别为浅潜型的秘鲁鲣鸟（Peruvian Booby, *Sula variegata*）以及深潜型的瓜纳伊鸬鹚（Guanay Cormorant, *Phalacrocorax bougainvilliorum*）；同时还包含其主要猎物秘鲁鳀（Peruvian anchoveta, *Engraulis ringens*）的丰度与垂直深度分布数据。基于这一独特数据集，我们构建了资源选择函数，以检验如下假说：海鸟在特定区域发生潜水行为的概率，取决于上层水体中猎物的相对丰度。
3. 对于两种海鸟而言，其潜水行为发生概率主要由浅层分布的猎物格局所解释。尽管在猎物丰度较低的区间内，潜水行为发生概率会随猎物丰度提升而急剧升高，但仅加入猎物丰度（而非仅依赖其深度分布）的模型支持度较弱，这表明在本研究周期内，猎物丰度并非决定潜水行为发生位置的核心因素。
4. 本研究由此凸显了猎物深度分布对于两种潜水能力迥异的海鸟物种的重要性。研究结果佐证了此前的相关结论——即提升猎物可获取性的海洋水文过程（oceanographic processes）至关重要。这一发现的启示在于：对于海鸟这类表层觅食者而言，猎物可稳定出现在适宜深度的区域，相比猎物丰度较高但深度不适宜的区域，其生态价值更为突出。
5. 解析丰度与可获取性的相对重要性，对于设计并评估针对海鸟及其他海洋顶级捕食者的猎物可获取性下降问题的有效管理对策，具有关键指导意义。